Physics - W.E.P. Question with Solution | TestHub

The block descends as the string shortens. Initially the string from ring to pulley has length h/cos60 = 2h; when the string becomes vertical its length is h, so the block falls by h. The block's speed equals the rate of shortening of the string, v_block = v_ring sin(theta); as the string becomes vertical theta -> 0, so the block's speed tends to zero at that instant. Energy conservation: mgh = (1/2) m v^2, giving v = sqrt(2gh). Answer: (B).